What Defines a Host? Oviposition Behavior and Larval Performance of Spodoptera frugiperda (Lepidoptera: Noctuidae) on Five Putative Host Plants

Lethal and sublethal effects of cotton expressing single and pyramided proteins of Bacillus thuringiensis (Bt) on Helicoverpa armigera (Lepidoptera: Noctuidae), Spodoptera litura (Lepidoptera: Noctuidae), and Spodoptera frugiperda (Lepidoptera: Noctuidae)

The susceptibility to proteins from Bacillus thuringiensis (Bt) can vary among lepidopteran pest species. While Bollgard 3 cotton (BG3) effectively controls the primary pest Helicoverpa armigera (Hübner) in Australia, its effectiveness against other pests, such as Spodoptera litura (Fabricius) and Spodoptera frugiperda (J. E. Smith), is unknown. This laboratory study assessed the survival and development of H. armigera, S. litura, and S. frugiperda larvae when fed foliage from a non-transgenic cotton variety (CC) and 3 transgenic cotton varieties: Bollgard (BG1) expressing Cry1Ac, Bollgard II (BG2) expressing Cry1Ac and Cry2Ab, and Bollgard 3 (BG3) expressing Cry1Ac, Cry2Ab, and Vip3A. Pyramided Bt cotton had greater negative effects on survival and development of all species compared with CC or BG1. The proportion of H. armigera that eclosed as adults was very low when larvae fed on BG2 or BG3 compared with BG1. Eclosion rates of S. litura and S. frugiperda on BG3 were much lower compared with BG2 and BG1. This study demonstrates that BG3 has greater efficacy against a wider lepidopteran pest complex compared with previous Bt cotton products. Despite efficacy in the laboratory, S. litura larvae are reported to be surviving in BG3 fields, suggesting other factors are influencing field efficacy. As BG3 production expands across tropical northern Australia, preserving the susceptibility of S. litura and S. frugiperda to BG3 proteins is crucial. This study identifies the need for further research on field survival and resistance management strategies for secondary pest species.

Morphogenetic Identification of a New Record Condica capensis (Lepidoptera: Noctuidae) in Yunnan, China

Condica capensis (Lepidoptera: Noctuidae), a newly identified pest in Yunnan Province, China, poses a threat to safflower crops. Discovered in Nanhua County in November 2023, the pest damages safflower at multiple life stages, especially during its larval stage, when it feeds on leaves, tender stems, and flower filaments, sometimes causing the entire plant to die. Morphological and molecular analyses, including mitochondrial cytochrome C oxidase I (COI) gene sequencing, confirmed its identity as C. capensis, a new species record for Yunnan. The study also documented the pest's life cycle, reproductive behavior, and natural enemies, highlighting the potential for biological control using parasitic wasps such as Cotesia sp. This research emphasizes the need for accurate pest identification and monitoring to develop effective, sustainable pest management strategies. As safflower cultivation grows in Yunnan, managing C. capensis is critical to safeguarding local agriculture and preventing broader agricultural threats.

Molecular evidence for the role of the ovipositor of the fall armyworm: Where to lay or not to lay?

Oviposition behavior in insects has received considerable attention, but studies have mainly focused on the antennae, neglecting the role of the ovipositor. In this study, we investigated the functional characteristics of the ovipositor in oviposition site selection by the fall armyworm (FAW) Spodoptera frugiperda, a destructive invasive pest of maize and other cereals. In oviposition choice assays females exhibited significant repellency to isothiocyanate (ITC), volatiles specific to non-preferred cruciferous plants. Females retained repellency to ITC or attraction to maize volatiles even after antennae removal. Scanning electron microscopy indicated the presence of olfactory-associated sensilla on the ovipositor. Comparative transcriptome analysis and in vitro functional studies showed that S. frugiperda odorant binding protein 30 (SfruOBP30), exclusively expressed in the ovipositor, displayed a broad sensitivity toward 18 maize volatiles and 10 ITC compounds. Site-directed mutant assay revealed that Ser71 and Ser85 were the key binding sites for SfruOBP30 interacting with ITCs and key maize volatiles, respectively. Silencing the expression of SfruOBP30 resulted in the loss of bias in oviposition of FAW, significantly inhibiting their ability to avoid ITCs and locate the maize substrate. Overall, we propose that the ovipositor does not just seek out advantageous conditions for immature stages but more importantly, avoids potential risks during the oviposition process. Apparently, the involvement of SfruOBP30 plays a critical role in detecting both beneficial and harmful substances during this intricate process.

The Effect of Wood Ash and Soil Applications on the Behavior and Survival of Spodoptera frugiperda (Lepidoptera: Noctuidae) Larvae on Maize

Cryptic feeding inside maize whorls makes it difficult to control fall armyworm (FAW). Smallholder farmers use alternative methods of control, of which the efficacy is uncertain. We determined the efficacy of wood ash and soil for the control of FAW and recorded its effect on larval preference and ballooning. Maize plants were artificially infested with larvae of different instars and treatments were either soil, wet ash, or dry ash, applied as single preventative or curative applications. Larvae exhibited non-preference for treated leaves in choice tests. The efficacy of treatments varied largely between experiments. Under laboratory conditions, ash treatments resulted in significant mortality of 1st and 5th instars. Dry and wet ash as curative applications for 1st instars resulted in 67 and 66% mortality, respectively, compared to mortality recorded in the control (22%). Under field conditions, survival of 3rd instars on treated plants was low (21-34%), compared to 70% on untreated plants. Due to the high variability in efficacy, the use of these alternative methods does not guarantee effective control. They do, however, have a place in IPM systems if applied as soon as infestations are observed and when larvae as still small. Recommendations on the use of ash and soil as spot treatments against FAW are provided.

Dispersal Behavior Characters of Spodoptera frugiperda Larvae

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a major pest of corn worldwide. FAW larval dispersal is an important life strategy that influences FAW population distribution in corn fields and subsequent plant damage. We studied FAW larval dispersal in the laboratory with sticky plates placed around the test plant and a unidirectional airflow source. Crawling and ballooning were the main dispersal means of FAW larvae both within and between corn plants. All larval instars (1st-6th) could disperse by crawling, with crawling being the only dispersal mechanism for 4th-6th instars. By crawling, FAW larvae could reach all aboveground parts of a corn plant as well as adjacent corn plants where leaves overlapped. Ballooning was used primarily by 1st-3rd instar larvae, and the proportion of these larvae that used ballooning decreased with age. Ballooning was largely governed by the larva's interaction with airflow. Airflow influenced the direction and distance of larval ballooning. With an airflow speed of about 0.05 m/s, 1st instars could travel up to 196 cm from the test plant, indicating that long-distance FAW larval dispersal depends on ballooning. These results increase our understanding of FAW larval dispersal and provide scientific information for the development of FAW monitoring and control strategies.

Helicoverpa armigera preference and performance on three cultivars of short-duration pigeonpea (Cajanus cajan): the importance of whole plant assays

BACKGROUND

Helicoverpa armigera is a major pest of pigeonpea (Cajanus cajan). Efforts to develop pigeonpea varieties resistant to H. armigera attack have been met with limited success, despite reports of high levels of resistance to H. armigera in wild relatives of pigeonpea and reports of low to moderate levels of resistance in cultivated varieties. Here we examined H. armigera oviposition preference and larval performance on whole plants of three cultivars of short-duration pigeonpea: a susceptible control (ICPL 87) and two cultivars with purported host-plant resistance (ICPL 86012 and ICPL 88039).

RESULTS

In our no-choice oviposition experiment, H. armigera laid similar numbers of eggs on all three cultivars tested, but under choice conditions moths laid slightly more eggs on ICPL 88039. Larval growth and development were affected by cultivar, and larvae grew to the largest size (weight) and developed fastest on ICPL 86012. Moths laid most of their eggs on floral structures, sites where subsequent early instar larvae overwhelmingly fed. Experimentally placing neonate larvae at different locations on plants demonstrated that larvae placed on flowers experienced greater survival, faster development, and greater weight gain than those placed on leaves. The type and density of trichomes (a potential resistance trait) differed among cultivars and plant structures, but larvae selected to feed at sites where trichomes were absent.

CONCLUSION

Future work examining host-plant resistance against H. armigera should incorporate the behavioural preference of moths and larvae in experiments using whole plants as opposed to bioassays of excised plant parts in Petri dishes. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A Special Collection: Spodoptera frugiperda (Fall Armyworm): Ecology and Management of its World-Scale Invasion Outside of the Americas

The Special Collection 'Spodoptera frugiperda (fall armyworm): Ecology and Management of its World-scale Invasion Outside of the Americas' presents reviews and research that address topics of overarching interest and contributes to a better understanding of this pest and its management, now that it has spread outside the Americas. The collection is a combination of invited articles presenting new information published for the first time, invited review papers, and a selection of relevant high-quality articles previously published in Journal of Economic Entomology (JEE). Articles in the Collection, as well as selected citations of articles in other publications, reflect the increase in research on S. frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), which became the most important pest of maize in the world during recent years. This Special Collection addresses a wide range of topics, including pest behavior, host strains, insecticide and Bt protein resistance, biological control, host plant resistance, and yield loss estimates. Topics are presented in context of research primarily conducted in regions outside of the Americas where S. frugiperda has invaded and disrupted crop production to varying degrees. In recognition of further spread, the threat of a S. frugiperda invasion into Europe and potential management options are also presented.